Knife sharpener



Jan. 7, 1969 F. w. WATERMAN nl KNIFE SHARPENER Filed July 14. 1966 FfederlcK LJ we'efrhw 1U INVENTOR.

United States Patent Oiiice 3,420,123 Patented Jan. 7, 1969 4 Claims ABSTRACT F THE DISCLOSURE A knife Sharpener comprising an elongated tapered dense non-porous sntered alumina ceramic rod containing at least 85% by weight aluminum oxide and having a surface finish not greater than about 60 microinches.

This invention relates to an improved knife Sharpener of the type used by meat cutters, commonly referred to as a steel, and consisting of an elongated tapered Sharpener rod with a handle secured to the large diametered end thereof such that the sharpener can be held and a knife edge stropped against the rod.

Knife Sharpeners of the type described are conventionally formed of a hard metal rod with a cross-hatched or knurled surface. Actually, this conventional construction is not in a true sense a knife Sharpener since as the knife edge is stropped thereagainst it is not really sharpened but rather only straightened. This is evidenced by the fact that professional meat cutters, albeit they repeatedly use such conventional steels during the course of each days work, nevertheless must have their knives periodically truly sharpened in order to obtain a fresh sharp edge.

It is an object of the present invention to provide an improved knife-sharpener of the type described wherein the Sharpener tool performs a true knife edge sharpening as well as a knife edge straightening function. Another and attendant object of the invention is provision of an improved knife ySharpener of the type described which is both durable and efiicient and which is simple of construction and hence easy and inexpensive to manufacture. Still another object is the provision of an improved method for sharpening knives.

Briey, these objects are accomplished in accordance with the invention by a knife Sharpener wherein the elongated tapered Sharpener rod is formed of a sntered alumina ceramic containing upwards of about 85% aluminum oxide and consisting essentially of aluminum oxide crystals bonded together into a dense unitary nonporous body. The aluminum oxide crystals of the body can be bonded to each other either directly or through the medium of an intercrystalline glassy phase formed in situ during the sintering operation in the manufacture of the body by reason of the interaction of the ceramic ingredients included. A knife Sharpener body of such composition and structure demonstrates not only true knife sharpening action but also has the other requisite properties essential for a practical durable efiicient use including, for example, the requisite toughness to insure against breakage from relatively rough handling. Actual tests performed by use of such knife Sharpeners by professional meat cutters in the day-to-day practice of their profession has demonstrated that there is a true knife sharpening action, the cutting edges of the knives thereby being continuously maintained sharp and hence dispensing with the need for periodic edge renewal by other means.

Other objects, features and advantages of the invention will appear more clearly from the following detailed description of preferred embodiments thereof made with reference to the drawing which shows a side view in partial section of a knife-Sharpener made in accordance with the invention.

Referring to the drawing, 1 is the elongated tapered knife Sharpener rod and 2 is the handle secured to the large diametered cylindrical end 3 of the rod. For reasons hereinafter mentioned, the prefenred means for securing the rod to the handle is by way of a cement or resin, such as epoxy resin 4, which permanently bonds the two members together. The handle 2 can of course be made of wood, plastic or other material as desired. The length of the rod, from handle to tip, should be upwards of 10 inches, generally about 12 inches, and the diameter adjacent the handle can be on the order of 1/2 to 3%: inch.

In accordance with the invention, the rod 1 is a sntered alumina ceramic containing upwards of by Weight aluminum oxide. Where the body consists of less than aluminum oxide, the remaining ingredients can be any of a variety of other oxides or mixed oxides or the like which by interaction with surface portions the aluminum oxide gains during the sintering operation function as glass forming ingredients to provide an intercrystalline glassy phase, or as mineralizers to control alumina crystal grain growth. Examples of preferred ingredients which can be used as additives to the alumina are: silica either as such or in one of its combined forms such as clay (aluminum silicate) or talc (magnesium silicate); the alkaline metal and alkaline earth metal oxides, silicates, carbonates and phosphates; other of the metal oxides either as glassy phase modifiers or as mineralizers, such as manganese oxide, chromium oxide, cobalt oxide and the like. Specific examples of high alumina ceramic compositions useful for the practice of the invention are as follows, the percentages specified always being by weight: 100% aluminum oxide; 99.5% aluminum oxide, .5% chromium oxide; 94% aluminum oxide, 3% silica, 3% magnesium oxide; 90% aluminum oxide, 4% silica, 3% calcium oxide, 3% talc; 85% aluminum oxide, 10% clay, 5% calcium oxide. To process such compositions into a sntered unitary dense nonporous rod the ceramic raw batch ingredients are first milled to a fine powder batch, preferably of a particle size no larger than 325 mesh, which is then compacted to the desired elongated tapered shape and then fired to sintering temperature which can be from 1400o C. to as high as l900 C. depending upon the precise composition. Shaping of the raw batch powder into the elongated tapered shape desired is preferably accomplished by admixing with the ceramic powder a temporary organic binder such as wax or organic resin and then molding to shape. The temporary organic binder is, of course, vaporized or burned out in the early stages of the sintering operation. Where the composition is 100% aluminum oxide or an extremely high percentage of aluminum oxide with only a small amount of additive other oxide as a mineralizer or the like, generally relatively high firing temperatures must be used to accomplish sintering and the final `structure is one wherein the alumina crystals are bonded directly to each other. Where a lesser amount of aluminum oxide is included, along with glass forming ingredients, generally somewhat lower firing temperatures may be used and the final structure consists of aluminum oxide crystals with an intercrystalline glassy phase which is formed in situ fby interaction of the ingredients during the sintering operation. There is shrinkage during the firing operation, on the order of 10% to 30% and hence the rod prior to firing should be larger than the final rod desired.

Such high alumina bodies, sntered to dense non-porous construction, are extremely hard and tough as compared with other ceramics and even though the surface of the body is relatively smooth and Without knurling, crosshatching or the like, demonstrates a marked ability to actually sharpen as well as ystraighten a knife edge stropped thereagainst. The Wear resistance of the surface is such that there is practically no wear from repeated continued use, and hence it is practical and desirable for inexpensive manufacture to permanently secure the handle 2 to the sharpened body 1 by way of a bonding resin or cement rather than go to the added expense of providing a detachable securement of the body to the handle so that the body can be replaced when worn. The toughness of the alumina ceramic is sufficient that the body can take normal abuse without breakage. As alluded to above, the excellent sharpening characteristics of the body are not dependent upon the provision of a rough surface nish, as is generally characteristic of other types of ceramic-like materials when used for metal sharpening. Surface finishes on the order of to 60 microinches (arithmetic average) are characteristic of dense nonporous sintered alumina rods made in accordance with the invention, and such surface finishes have been found excellent in performing the knife sharpening function. As a matter of fact, rougher surface finishes are undesirable in that to 'be accomplished in a practical and inexpensive way, they generally Ainherently involve an increase in porosity and hence a reduction in the density of the ceramic, and an extremely dense non-porous cer- -amic structure is important to knife Sharpener of the present invention to provide the necessary toughness to withstand normal abuse, The density of the alumina ceramic body 1 should be at least about 3.6 g./ cc. which means thatt he ceramic is substantially non-porous since the theoretical highest density for alumina ceramic is 4 g./cc.

The applicant makes no claim to the above alumina compositions per se. To the contrary, the particular compositions and the various additives specified above have been given only by way of example, these and other high alumina compositions and additives therefore being well-known in the ceramics art. What is claimed as the invention here is a novel and inobvious knife Sharpener,

and method, incorporating such high alumina ceramic and providing an unexpectedly excellent combination of properties, for knife sharpening, including the true ability to sharpen as Well as straighten a knife edge together with the requisite toughness and wear resistance to provide durability both in normal use and in situations of normal expected abuse as where the knife, instead of being carefully stropped against the rod, is carelessly stropped as in such a manner as would be expected to induce breakage.

While the invention has been described specifically with reference to certain embodiments thereof, it will be understood that various changes and modifications may be made all within the full and intended scope of the claims Which follow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A knife Sharpener comprising an elongated dense non-porous sintered alumina ceramic rod containing at least by weight aluminum oxide and having a tapered portion with a surface finish not greater than about 6() microinches.

2. A knife Sharpener as set forth in claim 1 wherein said rod has a density of at least about 3.6 grams per cubic `centimeter and a surface finish of from about 20 to 60 microinches.

3. A knife Sharpener as set forth in claim 1 wherein said rod has a handle secured to the large diametered end thereof.

4. A knife Sharpener as set forth in claim 3 wherein said handle is permanently bonded to said rod.

References Cited UNITED STATES PATENTS 1,888,102 11/1932 Zahler 76--84 2,730,439 1/1956 Houchins 51-206 XR 2,907,148 10/1959 Sheets 51-206 2,988,933 6/1961 Buck 76-84 GRANVILLE Y. CUSTER, IR., Primary Examiner. 

